The present invention relates to a device for controlling the opening and closing of a fluid valve, such as a liquid or gas valve, and in particular to such a device which operates on lever principles.
As is well known, the controlling of the opening and the closing of many fluid valves is accomplished by a double lever-fulcrum system. In such a system, a longer or power lever is rigidly fixed with respect to a shorter or thrust lever, and the two levers are interconnected to pivot about a fulcrum. Therefore, a relatively slight amount of force exerted on the longer or power lever results in a relatively greater amount of force being applied by the shorter or thrust lever. It is necessary for the force applied by the thrust lever, in controlling a fluid valve, to be of sufficient strength to counteract the pressure of the fluid. Such double lever-fulcrum control devices are known to be operated by devices such as a float for controlling a liquid, or a tension spring for controlling a gas.
The effectiveness of such a double lever-fulcrum control device depends upon the ratio between the lengths of the longer and shorter levers. Specifically, the higher this ratio, the smaller the force which need be applied on the longer or power lever. Consequently, the higher such ratio, the smaller may be the size of the float (in the case of liquids) and the smaller may be the tension and size of the spring (in the case of gases).
It is of course obvious that the shorter or thrust lever must have the smallest possible length. However, in practice, the smaller the length of the thrust lever, the smaller is the space available for positioning the usual pin or shaft of a sufficient diameter for being employed as the fulcrum of the device. As the fulcrum shaft is made smaller, it of course becomes weaker, and the entire device is thus more susceptible to normal operating stresses.